Method for producing an aqueous acrylamide solution with a biocatalyst

ABSTRACT

The invention relates to a method and device for producing an aqueous acrylamide solution by hydrating acrylonitrile in an aqueous solution while in the presence of a biocatalyst.

The present invention relates to a method and a device for producing anaqueous acrylamide solution by hydrating acrylonitrile in an aqueoussolution in the presence of a biocatalyst.

The conversion of acrylonitrile into acrylamide in the presence of asuitable biocatalyst in water has been known for many years and isdescribed, for example, in DE 30 17 005 C2, whereby in this method thebiocatalyst is immobilised. DE 44 80 132 C2 and EP 0 188 316 B1 describespecial biocatalysts for the conversion of acrylonitrile intoacrylamide. U.S. Pat. No. 5,334,519 teaches the hydration ofacrylonitrile to form acrylamide in the presence of biocatalysts andcobalt ions. All these teachings have the drawback that the biocatalystis damaged during the reaction so that its activity is reduced or thereis an increased formation of undesirable by-products.

Therefore, it is the object of this invention to provide a method inwhich the biocatalyst is damaged as little as possible during thereaction, by-products are minimised and the batch time is optimised.

According to the invention, the object is achieved by a method forproducing an aqueous acrylamide solution by hydrating acrylonitrile inan aqueous solution in the presence of a biocatalyst during which thereaction mixture is mixed, the reactor comprising a pumping circuit inwhich a part of the reaction mixture is circulated by means of a pumpand in which at least one heat exchanger is arranged.

At the start of the reaction, deionised water and the biocatalyst areplaced in the reactor and brought to a temperature of 15 to 25° C.,preferably 16 to 20° C. When the temperature is reached, theacrylonitrile is added to the reactor and conversion to acrylamidecommences. Preferably, the entire conversion takes places isothermally.At the start of reaction, the concentration of the biomass, expressed assolids, is preferably 0.03-2.5 g/l, particularly preferably 0.05-1 g/land the pH value is preferably 6.0-8.0, particularly preferably 6.5-7.5.

Preferably, an agitating element with an intensive action is arranged inthe reactor with which the reactor content is homogenously mixed. In apreferred embodiment, the reactor comprises external half-pipe coilswith which the reaction mixture can be additionally cooled during theconversion of acrylonitrile into acrylamide.

According to the invention, the reactor has a pumping circuit in which apart of the reaction mixture is circulated by means of a pump. Arrangedin this pumping circuit is at least one heat exchanger with which thereaction heat may be drawn off. Preferably, the heat exchanger is ashell-and-tube heat exchanger in which advantageously the reactionmixture is not diverted in order to avoid fouling on the heat exchangersurfaces.

In a preferred embodiment of the invention, the pump and the heatexchanger(s) are designed to ensure the avoidance of, on the one hand,temperature fluctuations in the reactor and, on the other, excessiveenergy input from the pump. Preferably, the pump is a magneticallycoupled side channel pump.

Advantageously, the addition of the acrylonitrile to the pumping circuitis very particularly preferably performed directly before the re-entryof the reaction mixture into the reactor. The addition is preferablyperformed continuously. A frequency-controlled piston-diaphragm pump hasbeen found to be particularly advantageous as the feed pump for theacrylonitrile.

When the addition of the acrylonitrile is completed, a secondaryreaction of preferably 4 to 20 minutes, particularly preferably 5 to 10minutes, is required to convert the acrylonitrile as completely aspossible. During this secondary reaction time, it is advantageous forthe cooling to be successively reduced with the bypass.

To optimise the performance of the reaction, the course of the reactionin the reactor is advantageously monitored by means of on-linemeasurement. This measurement enables the performance of the reaction tobe adapted very quickly in response to any possible changes. Preferably,the on-line measurement is performed in the pumping circuit before theacrylonitrile feed point and preferably, the acrylonitrile and/or theacrylamide concentration are continuously monitored.

On-line measurement with a Fourier transform infrared device (FT-IRdevice) has been found to be advantageous.

The results of the on-line measurement may be used to control theconversion. Advantageously, the quantity of acrylonitrile added, thevolume of the pumped flow, the bypass volume and the secondary reactiontime are controlled.

The method according to invention may be performed with any biocatalystthat catalyses the conversion of acrylonitrile into acrylamide.Preferably, however, the biocatalyst is a Rhodococcus rhodochrousdepsited under the deposition number 14230 with DSMZ, Deutsche Sammlungvon Mikroorganismen und Zellkulturen GmbH (German Collection ofMicroorganisms and Cell Cultures Ltd), Mascheroder Weg 1b, D-38124Braunschweig, Germany.

The method according to the invention has the advantage that during theconversion of acrylonitrile into acrylamide, the biocatalyst is damagedas little as possible and therefore the quantity of biocatalyst to beused is minimised, fewer by-products are produced, the conversion of theacrylonitrile takes place at least almost completely and that anacrylamide solution of up to 50% by weight is achievable. The methodaccording to the invention is simple and inexpensive to perform. Themethod according to the invention enables the reaction times to bedrastically reduced. The biocatalyst is utilised to the optimum extent.

The method according to the invention is preferably performed in adevice for the production of an aqueous acrylamide solution by hydratingacrylonitrile in an aqueous solution in the presence of a biocatalystwith a reactor, a pumping circuit in which a part of the reactionmixture is circulated by a pump and at least one heat exchanger arrangedin the pumping circuit. Therefore, this device is a further subject ofthis invention.

Preferably, an agitating element with an intensive action is arranged inthe reactor with which the content of the reactor is homogeneouslymixed. In a preferred embodiment, the reactor comprises externalhalf-pipe coils with which the reaction mixture may be additionallycooled during the conversion of acrylonitrile into acrylamide.

According to the invention, the reactor has a pumping circuit in which apart of the reaction mixture is circulated by means of a pump. Arrangedin this pumping circuit is at least one heat exchanger with which thereaction heat may be drawn off. Preferably, the heat exchanger is ashell-and-tube heat exchanger in which the reaction mixture isadvantageously not diverted in order to prevent fouling on the surfacesof the heat exchanger.

In a preferred embodiment of the invention, the pump and heatexchanger(s) are embodied to ensure the avoidance of, on the one hand,temperature fluctuations in the reactor and, on the other, excessiveenergy input from the pump. Preferably, the pump is a side channel pump.

Advantageously, very particularly preferably, the acrylonitrile is addedto the pumping circuit directly before the re-entry of the reactionmixture into the reactor. The addition is preferably performedcontinuously. A frequency-controlled piston-diaphragm pump has beenfound to be particularly advantageous as the feed pump for theacrylonitrile.

When the acrylonitrile has been added, a secondary reaction ofpreferably 4 to 20 minutes, particularly preferably 5 to 10 minutes, isrequired to convert the acrylonitrile as completely as possible. Duringthe secondary reaction time, it is advantageous for the cooling to besuccessively reduced with at least one bypass.

To optimise the performance of the reaction, the course of the reactionin the reactor is advantageously monitored by means of an on-linemeasurement. This measurement enables the performance of the reaction tobe adapted very quickly in response to any possible changes. Preferably,the on-line measurement is performed in the pumping circuit before theacrylonitrile feed point and preferably, the acrylonitrile and/or theacrylamide concentration are continuously monitored.

On-line measurement with a Fourier transform infrared device (FT-IRdevice) has been found to be advantageous.

The results of the on-line measurement may be used to control theconversion. Advantageously, the quantity of acrylonitrile added, thevolume of the pumped flow, the bypass volume and the secondary reactiontime are controlled.

The device according to the invention has the advantage that during theconversion of acrylonitrile into acrylamide, the biocatalyst is damagedas little as possible and therefore the quantity of biocatalyst to beused is minimised, fewer by-products are produced, the conversion of theacrylonitrile takes place at least almost completely and that anacrylamide solution of up to 50% by weight is achievable. The deviceaccording to the invention is simple and inexpensive to operate. Themethod according to the invention enables the reaction times to bedrastically reduced. The biocatalyst is utilised to the optimum extent.

The invention will be further described with reference to FIG. 1.However, these explanations are by way of example only and do notrestrict the general concept of the invention.

FIG. 1 is a schematic diagram of the method according to the inventionor parts of the device according to the invention. Before the start ofthe actual conversion of acrylonitrile into acrylamide, deionised water1 and a suspension 2, containing the biocatalyst, are placed in thereactor 3. The content of the reactor 3 is mixed homogenously with amotor-driven agitator 16. On the exterior of the reactor 3 there arecooling coils 17 which are connected to the cold water inlet 5 and thecold water outlet 4. A person skilled in the art will recognise thatthese cooling coils can also be used to heat the reactor content to aspecific temperature before the start of the actual reaction.

In addition, the reactor 3 comprises a pumping circuit 18 through whicha part of the reactor content is circulated by means of the magneticallycoupled side channel pump 7. Arranged in the pumping circuit 18 arethree shell-and-tube heat exchangers 6 connected in parallel with whichthe reactor content may be heated or cooled. The heat exchangers 6 arealso connected in series to the cold water inlet or outlet. In addition,the pumping circuit comprises the bypass 15 with which the heatexchanger 6 may be bypassed. The corresponding valves are not shown. Thepumping circuit also contains the Fourier transform infrared device(FT-IR device) 9 for the on-line measurement of the acrylonitrile andacrylamide concentration in the circulated flow 18 and hence in thereactor 3. The sample flow is taken from the pumping circuit 18 and sentby means of the piston-diaphragm pump 8 to the FT-IR device 9 where itis analysed. The analytical data are used to control the method. Shortlybefore the pumping circuit 18 re-enters the reactor 3, the acrylonitrileto be converted is added thereto from the acrylonitrile receiver 10 bymeans of the diaphragm-feed pump 11. The acrylonitrile receiver 10 andthe reactor 3 are connected to each other by means of a pendulum line 19at the gas side. The line 19 is opened before the addition of theacrylonitrile commences and closed again when the addition is completed.When the reaction has finished, the aqueous acrylamide is separated fromthe biomass by means of an annular gap centrifuge 12 and the aqueousacrylamide collected in the receiver 13 and the biomass in the receiver14.

1. A method for producing an aqueous acrylamide solution, comprising:forming a first mixture by mixing water and a biocatalyst in a reactor;circulating the first mixture through the reactor and a pumping circuitwith a pump, wherein the pumping circuit has at least one heat exchangerand a circuit with which said heat exchanger may be bypassed;continuously adding acrylonitrile to the first mixture circulatingthrough the pumping circuit and the reactor at a location after the heatexchanger and directly before the reactor to form a reaction mixture;allowing the formation of acrylamide in said reaction mixture by thebiocatalyst that catalyzes the conversion of acrylonitrile and waterinto the aqueous acrylamide solution; cooling the reaction mixture bycirculating the reaction mixture through the reactor and said pumpingcircuit; and monitoring the course of the reaction by on-line measuringat least one of the acrylonitrile and acrylamide concentration flowingthrough the pumping circuit at a location before the addition of theacrylonitrile to the pumping circuit.
 2. The method according to claim1, wherein the heat exchanger comprises external half-pipe coils.
 3. Themethod according to claim 1, wherein the heat exchanger is ashell-and-tube heat exchanger.
 4. The method according to claim 1,wherein the pump is a side channel pump.
 5. The method according toclaim 1, wherein the acrylonitrile is added to the first mixture with afrequency-controlled piston-diaphragm pump.
 6. The method according toclaim 1, wherein the first mixture is brought to a temperature of from15 to 25° C. before adding the acrylonitrile to said first mixture. 7.The method according to claim 1, further comprising regulating thecooling of the reaction mixture by the heat exchanger by flowing thereaction mixture through the bypass after the acrylonitrile addition iscompleted.
 8. The method according to claim 1, further comprisingallowing the reaction to proceed for from 4 to 20 minutes after theacrylonitrile addition is completed.
 9. The method according to claim 1,further comprising allowing the reaction to proceed for from 5 to 10minutes after the acrylonitrile addition is completed.
 10. The methodaccording to claim 1, wherein the on-line measuring is carried out witha Fourier transform infrared (FT-IR) device.
 11. The method according toclaim 1, further comprising controlling the course of reaction based onsaid on-line measurement.
 12. The method according to claim 11, whereinat least one of (i) the amount of acrylonitrile added, (ii) the flowthrough the pumping circuit, (iii) the flow through the bypass, and (iv)a secondary reaction time, are controlled.
 13. The method according toclaim 1, wherein the biocatalyst is Rhodococcus rhodochrous, Deposit No.14230 at DSMZ, Deutshe Sammlung von Mikroorganismen und ZellkulturenGmbH, Mashroder Weg 1B, D-38124 Braunshwig, Germany.